its just small webm video files acts as trailer/preview, which gets swapped on hover images and starts to play...
ref :
http://image3.vod.pornhd.com/292/VAvJ8d4nXD/clip.webm
p.s. they dont have audio i guess.
count video length in seconds.,
seconds split in 4 parts
take each part count as starting point and + 5 seconds as ending point, which will create 4 , 5 secnods files , later join them and make them in webm and remove audio.
it can be implemented in your existing script/mechbunny, just need proper fmpeg comand.,